Field
The invention relates to the field of fiber optics. More particularly, it relates to the measurement of the fiber pathway in fiber optic systems.
Background
Fiber optics offers high data rate and electromagnetic interference immunity for data communications. While fiber optics was originally utilized for long distance links, fiber optics is now becoming prevalent in applications short distances links, for example within data centers, fiber-to-the-home (FIFTH), aircraft and ship-board. These systems would benefit from optical time domain reflectometer (OTDR) with high resolution to determine the precise location of fiber faults. OTDR operates by sending a short pulse of light into a fiber and measuring the round-trip time-of-flight from features in the fiber that reflect light. The measurement is often repeated many times and averaged to increase the accuracy of the measurement. The features may create relatively strong reflections from a precise point along the fiber path, such as the end of a polished fiber or contamination within a connector, which are referred to a ‘reflective events’ (RE). The REs may typically have reflection coefficient of −10 dB to −30 dB. Other features create little or no reflection ‘non-reflective events’ (NRE), such a Rayleigh back-scattering (RBS) or fiber bends that violate the minimum bend radius. The reflection coefficient of NREs typically is proportional to time duration of the pulse, or equivalently the distance spanned in the fiber by the pulse. The RBS may typically have a reflection coefficient of −70 to −100 dB/cm. Therefore, measurement of a RE and NRE with a resolution of 1 cm would require a receiver with a large dynamic range (60 dB to 90 dB).
There is a trade-off between the resolution of the OTDR (i.e., the ability to resolve the location of a fiber event) and the pulse length. The receiver amplifier can also limit the resolution, since a highly sensitive receiver (required to measure a NRE) can become saturated with the light returning from a RE. The saturation occurs because the optical receiver dynamic range is limited. Therefore, typical OTDR's are not capable of both high resolution and also high dynamic range.
Accordingly, various high sensitivity and high dynamic range systems and methods are described herein, that address the above and other limitations in the measurement community.